1. Technical Field
The present invention relates to an electrical device, and more specifically to a liquid metal micro-relay device.
2. Background Art
There are many different types of electrical micro-relay devices, and one popular type is the reed micro-relay, which is a small, mechanical contact type of electrical micro-relay device. A reed micro-relay has two reeds made of a magnetic alloy sealed in an inert gas inside a glass vessel surrounded by an electromagnetic driver coil. When current is not flowing in the coil, the tips of the reeds are biased to break contact and the device is switched off. When current is flowing in the coil, the tips of the reeds attract each other to make contact and the device is switched on.
The reed micro-relay has problems related to large size and relatively short service life. As to the first problem, the reeds not only require a relatively large space, but also do not perform well during high-frequency switching due to their size and electromagnetic response. As to the second problem, the flexing of the reeds due to biasing and attraction causes mechanical fatigue, which can lead to breakage of the reeds after extended use.
In the past, the reeds were tipped with contacts composed of rhodium or tungsten, or were plated with rhodium or gold for conductivity and electrical arcing resistance when making and breaking contact between the reeds. However, these contacts would fail over time. This problem with the contacts has been improved with one type of reed micro-relay called a “wet” relay. In a wet relay, a liquid metal, such as mercury, is used to make the contact. This solved the problem of contact failure, but the problem of mechanical fatigue of the reeds remained unsolved.
In an effort to solve these problems, electrical micro-relay devices have been proposed that make use of the liquid metal in a channel between two micro-relay electrodes without the use of reeds. In the liquid metal devices, the liquid metal acts as the contact connecting the two micro-relay electrodes when the device is switched ON. The liquid metal is separated between the two micro-relay electrodes by a fluid non-conductor when the device is switched OFF. The fluid non-conductor is generally high-purity nitrogen or some other such inert gas.
With regard to the size problem, the liquid metal devices afford a reduction in the size of an electrical micro-relay device since reeds are not required. Also, the use of the liquid metal affords longer service life and higher reliability.
The liquid metal devices are generally manufactured by joining together two substrates with a heater in between to heat the gas. The gas expands to separate the liquid metal to open and close a circuit. Previously, the heaters were inline resistors patterned on one of the substrates between the two substrates. The substrates were of materials such as glass, quartz, and gallium arsenide upon which the heater material was deposited and etched. Since only isotropic etching could be used, the heater element would consist of surface wiring. The major drawback of surface wiring is that such wiring has poor high-frequency characteristics, high-connection resistance, and poor thermal transfer to the gas.
More recently, suspended heaters have been developed. A suspended heater refers to a configuration in which the heating elements are positioned so that they can be completely surrounded by the gas.
Problems still exist with these liquid metal devices, which include difficulties with hermetically sealing the heaters.
The problems further include minimizing resistance throughout the liquid metal devices.
The problems still further include poor the high-frequency characteristics of the electrical path through the liquid metal devices.
The problems still further include problems related to poor impedance matching for high-frequency signals.
Solutions to these problems have been long sought, but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.